Ultramarine is a blue pigment, formula ideally Na7.5A16 S1 6024S4.5 manufactured by Reckitt's Colours Ltd. at a rate of >10,000 tonnes per annum. The structure is based on a sodalite cage and the pigment is manufactured from kaolin, sulphur, sodium carbonate and minor ingredients, in furnaces with small surface area to volume ratios. To simulate industrial furnacing while examining a sample by PXRD (Powder X-Ray Diffraction) a novel 'Birkbeck Cell' was developed for use in a Guinier-Lenng camera. This cell is based on a stainless steel former with mica windows, and together with a gas rinsing system this arrangement produced the first time-resolved PXRD study of ultramarine formation: kaolinite is first separately calcined to the amorphous phase metakaolinite, to which the sulphur and sodium carbonate are added; in the second part of the furnace cycle sulphur and sodium carbonate react to form a sodium polysulphide, with metakaolinite later reacting with sodium salts to form a carnegieite, which then combines with the sodium polysulphides to form the initial ultramarine lattice ('primary ultramarine') ; in the latter part of the furnacing an 'oxidation' stage forms blue ultramarine and sodium sulphate is produced as a by-product. These results are supported by differential thermal analysis and thermogravimetric analysis; model furnacing; room temperature PXRD studies of various components and stages in the process; visible/uv spectrophotometry and electron microscopy. The structure of ultramarine was refined by Rietveld analysis of the neutron powder diffraction data and showed that the aluminium and silicon are not .OW0 ordered, the space group is 143m , the sodium ions lie just off the six-fold faces and the S 3 - group is in the centre of the cage, in a disordered arrangement. This analysis is supported by magic-angle spinning nuclear magnetic resonance, PXRD and the current literature on other spectroscopic methods. Finally the role of minor ingredients is examined and initial experiments to indicate possible alternative manufacturing methods are described.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:311603 |
| Date | January 1987 |
| Creators | Tarling, Stephen Edward |
| Publisher | Birkbeck (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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